Not yet, say top executives from some of the world's leading power companies meeting in Houston for the last day of Cambridge Energy Research Associates' (CERA) annual energy conference.

The sheer amount of power the world uses presents a challenge to an industry striving to both double its power output and halve its greenhouse gas emissions over the next few decades.

"There's no question there are technical answers that can bring us clean energy," said Michael Morris, head of the utility American Electric Power (AEP, Fortune 500). "But the timeline is half a decade or a decade" away.

AEP is one of the largest users of coal - and one of the largest emitters of the greenhouse gas carbon dioxide - in the country.

Morris, like other power industry executives at the conference, said the country needs to push ahead in building electricity plants of all types if it is to meet its growing energy needs.

"If we don't do enough in every way we can, we'll find ourselves in a shortage," he said.

This fact presents a challenge for traditional power companies and an opportunity for clean and efficient energy technology, but executives were cautioning that their industry may not now be ready to embrace clean energy whole hog.

John Deutch, a former director of the Central Intelligence Agency under President Clinton and now an energy professor at Massachusetts Institute of Technology, echoed power executives' apprehension.

Specifically, he said technology to capture carbon dioxide from coal plants is not proven, and solar and nuclear are too expensive and unlikely to become cost-competitive anytime soon.

"My message has been overly pessimistic, in case you didn't notice," he joked, at the end of a 15-minute speech picking apart each technology. "I don't see much promise."

There's little doubt electricity that comes from cleaner sources - such as nuclear, solar, wind or cleaner coal - will end up costing consumers more money.

"Costs will be high across the spectrum of energy resources," said Jim Barry, chief executive of NTR, an Ireland-based operator of renewable energy projects. Barry added that European Union targets of achieving 20% of their power from renewable sources by 2022 "ain't going to happen."

Barry cautioned against - to borrow a phrase from Thursday night's keynote speaker Alan Greenspan - "irrational exuberance" when it comes to clean energy technology, and said to beware of "delusion and misinformation."